I believe that I have found a more specific answer to the clutch adjustment challenge on the old Edmund Scientific clock drive which have an unique and somewhat confusing clutch design. Here is my short story that may be of help:
I have updated my home built Cassegrain by adding a Crayford 10:1 focuser.
This led me to clean and restore my classic Edmund scientific 1"-shaft pedestal mount that has a vintage ES Clock Drive used exclusively with this scope.
I could not get the clutch to grip properly and was very frustrated. I did find this archived link doing a Google search on this very subject https://www.cloudyni...lutch-question/ on CN but it only took me part of the way.
What made this a bit more frustrating is that I actually have the original one-page Information and Instructions sheet that came with the clock drive with the revision number 3/77. It does not describe how the clutch adjustment is made or what tools are required.
However, I have been able to figure this out with the assistance of a friend who is an armature astronomer, engineer and machinist.
I offer this possible solution to all in case anyone has encountered the same issue. Since the archived subject is still available and covers most of the design of the clutch assembly portion of the drive, I will only focus on the important omission.
What seems to be missing is that the clutch is adjusted via 2 empty non-threaded holes (a picture of these holes and a 3/4 view of the drive itself for identification are attached). I have seen this drive using either long thumb screws or set screws (with hex nuts for locking, mine uses the latter).
Once you have everything inserted correctly (leather washer, AL disc without threaded center hole, AL disc with threaded hole and 2 set screws and finally AL disc with 2 adjustment set screws and 2 open holes) and have added tension to the 2 screws on the outer disc "locking" the last 2 discs together as one "lock nut" on the RA shaft, you would then need to use the 2 open non-threaded holes to make the clutch tension adjustment (NOT THE 2 SCREWS!). This is both counterintuitive and leaves out the need for a tool of some kind to make the necessary adjustment. I have found that these holes should be used as a viewing port to see the set screws on the center disc. If these sew screws move out of view while adjusting you then need to tension the outer screws until there is no movement.
Inserting 2 rods into these holes and spanning them with a large adjustable wrench would work or if you are handy you could make a simple tool yourself. If you have access to machining equipment this is very simple. I am surprised that this is neither mentioned in the original instructions nor is a tool mentioned at all. Actually, when reading the original instructions the adjustment procedure is covered by only one sentence and it is not clear.
Once you have a tool that can be inserted into the 2 open holes you can now add the final torque adjustment to fine tune the clutch.
The Tricky Part: Although, this is the key to the clutch adjustment, it requires some finesse. Turn your balanced scope on the RA by hand about 90 to 120 degrees clockwise and then counterclockwise from your center start point. If you feel that is is very loose you need to tighten the clutch using your new tool. If it loosens in one direction but tightens in the opposite direction your adjustment is too tight and you need to back the adjustment off a bit with your tool. There is an equilibrium point you need to find that allows a consistent tension on the clutch while turning your scope by hand (in either direction) yet applies enough tension to allow the clock drive to move your scope without slippage.
Testing: I tried testing the clutch adjustment by running the clock drive for 1 hour at a time and used blue tape on the shaft housing to identify movement. Once you have a coupe or more successful tests without the RA shaft tightening or loosening (in one direction) your set.
Since ES had no way of knowing what the size and weight of scope, counterweights and accessories would be used with these clock drives, I am amazed that they did not explain the clutch adjustment method more in-depth. One adjustment setting would not be applicable.
Okay, this worked for me and I hope that it works for you.
Edited by Vitez, 17 February 2021 - 07:22 PM.